Spontaneously broken mass

Abstract

The Galilei group involves mass as a central charge. We show that the associated superselection rule is incompatible with the observed phenomenology of superfluid helium 4: this is recovered only under the assumption that mass is spontaneously broken. This remark is somewhat immaterial for the real world, where the correct space-time symmetries are encoded by the Poincaré group, which has no central charge. Yet it provides an explicit example of how superselection rules can be experimentally tested. We elaborate on what conditions must be met for our ideas to be generalizable to the relativistic case of the integer/half-integer angular momentum superselection rule.

4 pages

References in corpus (3)

• Relativistic Fluids, Superfluids, Solids and Supersolids from a Coset Construction
• Low-Energy Quantum Effective Action for Relativistic Superfluids
• More on gapped Goldstones at finite density: More gapped Goldstones

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• An introduction to Goldstone boson physics and to the coset construction